<!DOCTYPE html>
<html><head>
<style>
#outer {
    opacity: 0.8;
    background-color:red;
    width: 200px;
}

#inner {
    opacity: 0.6;
    background-color:black;
    color:white;
}

</style>
</head>
<body>
  <div id="outer">
    <canvas width="200" height="200" style="display:block;" id="c1"></canvas>
    <div id="inner">
      <canvas width="200" height="400" style="display:block;" id="c2"></canvas>
    </div>
  </div>


<script>
var ctx = document.getElementById("c1").getContext("2d");
ctx.fillStyle = "black";
ctx.fillRect(0, 0, 200, 200);
var ctx = document.getElementById("c2").getContext("2d");
ctx.fillStyle = "black";
ctx.fillRect(0, 0, 200, 200);
ctx.fillStyle = "rgb(50,50,50)";
ctx.fillRect(0, 200, 200, 200);
</script>

</body></html>
